In their systematic review, Eslami et al acknowledged that CBCT imaging may be more effective than conventional radiography in canine impaction cases that are difficult to diagnose (Eslami E, Barkhordar H, Abramovitch K, Kim J, Masoud MI. Cone-beam computed tomography vs conventional radiography in visualization of maxillary impacted-canine localization: a systematic review of comparative studies. Am J Orthod Dentofacial Orthop 2017;151:248-58). Unfortunately, they may not have provided the best available evidence for making clinical decisions otherwise. The evidence allowing clinicians to evaluate when and how to incorporate cone-beam computed tomography (CBCT) imaging of ectopic canines in their practice for the benefit of their patients is missing.

The etiology of impacted canine-associated severe incisor root resorption (SIRR) is multifactorial, including both systemic and local factors. The risk for SIRR is increased for 3 reasons: (1) female patients with enlarged dental follicles and anomalous lateral incisors are more affected; (2) lateral incisors are affected more than central incisors, and the chance of bilateral occurrence is high; and (3) SIRR is found in both palatally and buccally impacted maxillary canines but may be associated with more severely displaced canines, situated in the middle third of the adjacent incisor roots.

The diagnostic problems and treatment risks associated with the alignment of impacted canines demand early detection of tooth eruption disturbances. They are of special importance for treatment planning in patients with impacted canines and root resorptions on adjacent teeth.

The use of radiologic imaging for impacted canines and their surroundings with low-dose conventional radiographs such as panoramic radiographs and intraoral radiographs (upper standard occlusal radiographs, paralleling technique periapicals) is limited by the issue to depict a 3-dimensional body in a 2-dimensional image. In certain cases, they do not correspond with the required accuracy and reliability.

Nevertheless panoramic imaging is indicated in a step-by-step approach. If the impacted canine cannot be imaged seperately and is projected on the mature roots of the adjacent teeth, the diagnosis of palpability of the crown of the permanent canine is not sufficient for excluding the threatening or already existing root resorption on the roots of the central or lateral incisors or the first premolars. Further radiographic views are needed. In the past, this was done using standard occlusal radiographs or paralleling technique periapicals. In many patients, especially when root resorption occurred in the sagittal plane, it could not be diagnosed on low-dose conventional radiography.

When the crown of the canine is superimposed on the roots of the adjacent teeth, the prevalence of root resorptions must be clarified. Complying with the SEDENTEXCT guidelines, further radiographic views should include CBCT or low-dose computed tomography radiography for the localized assessment of an impacted tooth when the current imaging method of choice is conventional dental radiography and when the information cannot be obtained adequately by lower-dose conventional radiography.

CBCT imaging has become the standard diagnostic tool in such cases by scientific findings, practical experience, and professional acceptance. For the localized assessment of an impacted tooth, including resorption of an adjacent tooth, the smallest volume size compatible with the situation should be selected because of reduced radiation dose.

The panoramic radiograph still remains an important part of initial diagnosis with the intention to reduce the need for additional CBCT imaging. It is used for determining the position of the impacted canine according to the sectors proposed by Ericson and Kurol ( Fig ).

Schematic illustration of the projection of the canine in the panoramic image and sectors (1 through 5) of the most medial position of the crown as originally proposed by Ericson and Kurol.

The mesiodistal position of the tip of the canine gives the clue for the degree of canine impaction and threatening or beginning root resorptions on adjacent teeth. The labiopalatal position of impacted canines and resorption of permanent incisors may be predicted using sector location on panoramic radiography.

Labially impacted canines are often found in sectors 5, 4, and 3; midalveolus impacted canines are more frequent in sector 2, and palatally impacted canines are more frequent in sector 1.

Canines in sectors 3, 2, and 1 increase the danger of potential root resorptions of the lateral and central incisors. The indication for CBCT imaging is given.

The eruptive movement or migration of the impacted canine during its root development process is likely to increase the risk of root resorption at adjacent incisors. Proximity less than 1 mm between the impacted canine and an adjacent root may be the most important predictor for root resorption.

Female sex, closed or dilacerated canine apex, vertical canine crown position less than 45° to the midline, and canine magnification were also strong predictors for root resorptions.

The presence of one of the above mentioned predisposing factors can be considered a helpful tool in justifying the need of additional CBCT or low-dose computed tomography examination.